The present invention relates to a rotational position detecting apparatus for supplying rotational angle signals as well as stable reference position signals.
Conventionally, electromagnetic sensors have been used frequently as the means of detecting rotational angles and the use of such sensor has given rise to such a problems as variation of the output with the rotational speed and the occurrence of magnetic interference when generating a composite signal. As a result, magnetically sensitive elements such as Hall devices or magneto-resistance elements have recently come into use. In a known rotational position detecting apparatus of the type employing such a magnetic sensing element, the magnetic field produced by a strong bias magnet is interrupted by a vane made of a magnetic material to thereby generate rotational position signals. However, this type is disadvantageous in that the number of output signals that can be produced for every revolution is small and the diameter of the apparatus is large. Further, if it is desired to supply any reference position signal in addition to the rotational position signals, a larger and more complicated apparatus will be required. Another known apparatus of the type comprising a magnetic disk magnetized to induce a large number of poles on its surface and magnetically sensitive elements for detecting purposes is also disadvantageous in that while it is possible to use the magnetic disk which is small in size but has a large number of poles, the surface magnetic flux density cannot be made so large and the output of the magnetically sensitive elements is low.